There is a pressing clinical need for an alternative to current therapeutic approaches to the problem of congestive heart failure. This application is directed towards establishing techniques whereby a suitable skeletal muscle may be diverted from its normal function and used instead to augment, or even replace, the function of a failing heart. This idea is not in itself new, but it has become possible to view it as a feasible approach only as a result of recent research into the long-term effects on adult mammalian skeletal muscle of an increase in functional demand. In particular, chronic low-frequency electrical stimulation of a muscle is now known to produce an adaptive transformation that includes marked increases in capillary density and mitochondrial volume, a correspondingly increased capacity for the generation of energy via aerobic pathways of metabolism, and a switch to the synthesis of slow-twitch isoforms of myosin. As a result of these changes, such a muscle becomes highly resistant to fatigue. The stimulation technique therefore offers a means of preconditioning a muscle to a state adapted to continuous use, overcoming the fatigue problem which was formerly the major obstacle to the use of skeletal muscle in myocardial assist devices. The proposed research plan includes evaluation of canine diaphragm, latissimus dorsi, pectoralis major, rectus abdominis and psoas major muscles for their suitability as actuators in three types of muscle-driven pump: hydraulic pouches; pocket pouches placed between a muscle and the chest or abdominal wall; and directly driven pumps. The plan includes the development of the totally implantable pump devices, and of stimulators for both conditioning the muscle grafts and using them to drive the pumps. The patterns of stimulation best suited to these purposes will be established in parallel experiments and their long-term effects investigated in detail. The work will culminate in the use of suitable muscles and implanted pump devices in vivo to drive asanguinous fluid around a closed hydraulic circuit for periods of up to one year. In this way, the technical and scientific basis will be established for developing the full clinical potential of this new approach to the treatment of cardiac failure.